水稲の稈の発育経過及び健全, 秋落型水稲間の稈内貯蔵澱粉消長の比較

抄録

With the same object as mentioned in our previous reports on the growing habit of leaf of rice plant, the present investigation was carried out to make clear the growing process of internodes of culm and seasonal changes of starch content in them according to their node order. The results obtained are summarized as follows: I. Growth process of internodes of culm. 1. Elongation process of the internodes of culm according to their order is shown in Fig. 1. 2. As shown in Fig. 2, the weight of total culm or each internode of culm increases gradually with the in development until it shows the 1st maximum weight at about 12 days after heading. Then it decreases gradually, and reaches to the minimum value at about 37 days after heading. From that minimum-weight time it increases slow lyagain till the ripening time. The 1st maximum-weight time shows the beginning of the growth process of grain and the minimum-weight time corresponds nearly to the finishing stage of its growth. II. Changes of the starch conteut in internodes of culm. 1. Seasonal changes of the starch content in each internode of culm of normal rice plant shows the same tendency as in the case of internode weight as shown in Fig. 3. The beginning of the decrease of starch content from the maximum condition is due to its vigorous translocation to panicle and, at the time of minimum starch content, the rice grain grows nearly into full weight and does not need more carholydrate. So, after this period, starch content begins to increase again untill the ripening time-secondary stage increase. One of the main causes that effect the change of weight of internodes is considered to be the change of the starch content in them. 2. Starch content in culm is generally higher in lower internodes and with the ascent of node order it tends to decrease. But, within the 13 th to 15 th internodes its difference is not so large. Only the 16th internode (the uppermost one) has very small content. 3. In "Akiochi" rice plant, the changes of starch content in accordance with its growth are as similar as in normal plant, but there is a same difference as in the absolute amount of starch accumulation from the normal one. 4. As shown in Fig. 4, the starch content in the lower internodes of "Akiochi" plant is much less than that in normal one, but from lower to the higher internodes the difference decreased gradually. In the uppermost internode (in lower part) and in the panicle stalk that finishes its growth at the later stage starch remains much more than in the normal one. Moreover, in the lower internodes of "Akiochi" plant, the secondary increase of starch is much less than in the normal one, starch accumulation not occuring at all especially in the upper internode and the panicle stalk. 5. The fact that the starch content in lower internodes of the "Akiochi" plant is lower than that in normal ones may be due to weaker carbon-assimilation and earlier translocation of carbohydrates from the internode to the panicle. The higher content of starch in the upper internodes and the panicle stalk of the abnormal plant comparred with that of the normal one may be due to the retardation of carbohydrate translocation from these parts to the panicle in later stages. These facts are altogether considered to cause the imperfect development of rice grains in "Akiochi" plants.